Waiting on the Moon

People on our street love to stop by and take a look through the telescope at the Moon, when it is in its waxing phase in the southern or western sky in the evening. A 9-year-old asked me the other night, “Have you ever looked at the Full Moon through your telescope?“ The answer is yes, of course, but then I had to explain to him that the Full Moon is probably the least interesting object to observe in the sky.

… which leads me to the more general topic: the Moon as the enemy of serious astronomers. Although it is one of the darkest objects in the solar system, reflecting only about 18% of the sunlight that falls on it, when it is above the horizon the Moon floods the sky with so much light that it is impossible for astronomers to see the faint galaxies, nebulae and star clusters that we are almost always aiming for when we get out our observing instruments – whether binoculars or telescopes. That is why astronomers love those weekends – which arrive every four weeks – when the Moon is at or close to its new phase. At these times the Moon sets around the same time as the Sun, and we get an entire night with no pesky light polluting orb in the sky.

This past weekend the weather forecast was that Thursday and Friday’s cloud cover would lift rather sharply just before midnight on Friday evening. The Moon was near First Quarter, and would set around 01.30 on Saturday morning. I drove up to our family cottage in Muskoka after work on Friday, had a quick supper, then went to bed for three hours, getting up around 22.00. Then I drove 90 km to the Torrance Barrens Deep Sky Preserve about 35 km southwest of Gravenhurst, set up the telescope and my photo equipment, and waited for the Moon to set and the sky to darken. Just after 1.30, with the temperature hovering at 6 degrees, I started making photos of the Milky Way. But then came the curse of late summer and fall: fog. At this time of year the combination of temperature changes and water vapour in the atmosphere often produces ground fog around and after midnight. At about 02.00, within one minute the entire sky filled with fog, and made continued observing impossible. So I reluctantly dismantled the telescope, loaded all of the gear into the car, and headed back to Toronto.

At least I got one set of photos that I was able to do something with. Here is a wide-angle photo of our Milky Way galaxy, consisting of three stacked 5-minute exposures (*see description below).

*The Milky Way – our home galaxy of billions of stars in a spiral disk – blazes across the late summer sky as seen from Torrance Barrens Dark Sky Preserve, Ontario, Canada. The three brightest stars of the “Summer Triangle” are Vega (upper edge, left of centre), Deneb (bottom left) and Altair (just above centre, toward right edge). Free hydrogen gas appears as reddish-magenta patches. The winding dark lanes are clouds of cold foreground gas that obscure the light from millions of stars that lie beyond.

The Moon will rule out the next two weekends for astronomy, so it’s time to go canoeing in Algonquin Park. The next good astronomy weekend will be Oct. 4-6, near New Moon.

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